A special interrogation team remains ready to question him as soon as he is able to talk.

As the investigation continues, police say based on the evidence they have already collected, the attack may have been planned to be even worse.

"Based on the evidence that was found at that scene, the explosions, the explosive ordinances that was unexploded and the fire power that they had, they were going to attack other individuals," Boston Police Commissioner Ed Davis said.

Investigators are taking a close look at the lives of the two brothers to seek a motive.

In 2011, CBS news reports the FBI questioned Tamerlan Tsarnaev after he was flagged. Those investigations surrounded a possible connection to Radical Islam.